Scuba Tank Sizes: Chart, Types, and How to Choose the Best for Your Di

2025 Scuba Tank Selection Guide: Common sizes are dominated by the Aluminum Tank AL80 (80 cubic feet / about 2265 liters, stores 179 liters of gas at 200bar working pressure) and the Steel Tank SC72 (72 cubic feet / about 2041 liters, lighter and corrosion-resistant). Tank selection needs to combine body weight (newcomers under 60kg are advised to use AL80, over 80kg or in cold water choose SC80), dive duration (AL80 supports about 60 minutes of recreational diving, deep diving requires SC100), and reference the PADI tank selection chart. Key is matching Volume × Pressure value (e.g., AL80 = 80 × 200 = 16000) to personal air consumption rate (generally 15-20 liters per minute for recreational diving).

How to Read Tank Sizes

To read scuba tank sizes, focus on two core data points: Capacity (liters) and Rated Pressure (bar). Common aluminum tanks include 12L (180-200bar pressure, stores about 2160-2400 liters of gas), 15L (2700-3000 liters); steel tanks are mostly 12L (200-300bar, 2400-3600 liters), 15L (3000-4500 liters). Gas storage volume = Capacity × Pressure (no complex conversion needed, larger number means longer duration).

Capacity and Pressure

The first step in choosing a scuba tank is understanding the two key numbers on the tank body: Capacity (liters, L) and Rated Pressure (bar). For example, a tank marked "12L/200bar" means the cylinder can hold a maximum of 12 liters of gas, and when pressurized to 200bar, it can store a total of 2400 liters of compressed gas. In actual diving, because a safety margin must be left (e.g., 10%-15%), the truly usable gas is only about 2000 liters.

Capacity

For example, a 12L tank is equivalent to compressing 12 liters of air into the cylinder. There are two main stream specifications for common scuba tank capacities: 12L and 15L.

12L tanks are the most common, especially aluminum models, suitable for most recreational divers.

The empty weight is about 14kg, and the full tank (200bar) is only about 50kg, making it easy to carry.

Based on a recreational diver's average consumption of 18 liters of gas per minute (10 meters deep, normal body temperature), a 12L/200bar tank with a total storage of 2400 liters, minus a 10% safety reserve leaving 2160 liters, can only support about 120 minutes (2 hours) of diving.

15L tanks are "oversized," with an empty aluminum 15L tank weighing about 17kg, and a full tank (200bar) weighing about 60kg.

Its total gas storage is 3000 liters, minus the safety reserve leaving 2700 liters, capable of supporting 150 minutes (2.5 hours) of diving.

It is suitable for frequent divers, or those going to cold water areas (e.g., water temperature below 15℃, where gas consumption may rise to 25 liters per minute). This is where the advantage of the 15L tank is demonstrated—for the same 2 hours of diving, it only requires 25 × 120 = 3000 liters of gas, and the 15L/200bar tank is just enough, avoiding the rush to surface.

Pressure

Pressure refers to the maximum internal gas pressure the tank can withstand, measured in bar (1bar ≈ 1 kilogram-force / square centimeter).

Common scuba tank pressures are divided into three levels: 180-200bar (mainstream for aluminum tanks), 200-250bar (some steel tanks), 250-300bar (high-pressure steel tanks).

A 12L tank at 200bar pressure can store 2400 liters of gas, while at 300bar pressure it can store 3600 liters—equivalent to adding 1200 liters of gas, allowing for an extra half hour of diving.

However, high-pressure tanks require higher material quality: aluminum tanks usually top out at 200bar because aluminum has good ductility but low strength, making it prone to deformation under high pressure; steel tanks can achieve 300bar, as steel is harder and can withstand higher pressures.

For example: a 12L/300bar steel tank has a total gas storage of 3600 liters, minus the safety reserve leaving 3060 liters.

If the diver is diving at a depth of 20 meters (3ata), the gas consumption per minute will increase to 18 × 3 = 54 liters (Boyle's Law: pressure doubles for every 10 meters of depth increase, and so does gas consumption).

At this point, 3060 liters of gas can support 3060 ÷ 54 ≈ 56 minutes, compared to the 12L/200bar aluminum tank (at the same depth, storage is 2400 × 1.5 = 3600 liters, with a reserve of 3060 liters, is it the same? This may require re-calculation: aluminum tank 12L/200bar, actual storage is 12 × 200 = 2400 liters, but at 20 meters depth (3ata pressure), the volume of this gas would expand to 2400 × 3 = 7200 liters? No, the diver breathes high-pressure gas from the tank, which is reduced by the regulator to the ambient pressure.

Therefore, gas consumption is calculated based on the regulator output pressure, for instance at 20 meters depth, the regulator outputs 3ata gas, the diver needs 54 liters per minute (18 liters/ata × 3ata), so the total gas consumption is 54 liters/minute × time = total gas volume in the tank (liters) × pressure in the tank (ata) ÷ ambient pressure (ata).

Perhaps a simpler way is: Total equivalent gas volume in the tank (ATA·L) = Capacity (L) × Pressure (bar) ÷ 1.013 (conversion to ATA).

For example, 12L/200bar aluminum tank, total equivalent = 12 × 200 ÷ 1.013 ≈ 2369 ATA·L.

At 20 meters depth (3ATA), usable time = 2369 ÷ (18 × 3) ≈ 44 minutes.

And 12L/300bar steel tank, total equivalent = 12 × 300 ÷ 1.013 ≈ 3554 ATA·L, usable time at the same depth = 3554 ÷ 54 ≈ 66 minutes. This is more accurate.

However, high-pressure tanks also have drawbacks: greater weight (12L/300bar steel tank empty is about 16kg, full tank is heavier), and require a dedicated high-pressure compressor for filling.

How to Calculate Gas Storage

To quickly know how long the tank can be used, remember this formula: Usable Time (minutes) = (Capacity × Pressure × 0.9) ÷ (Gas Consumption Per Minute × Depth Factor).

Capacity × Pressure = Total Gas Storage Volume (liters), multiplying by 0.9 is for deducting the 10% safety reserve.
Gas Consumption Per Minute: Recreational divers generally use 15-25 liters/minute (lower in calm water, higher in open water).
Depth Factor: Pressure doubles and gas consumption also doubles for every 10 meters of depth increase. For example, the factor at 10 meters depth is 2 (2ATA), and at 20 meters depth is 3 (3ATA).

Example: A 65kg recreational diver plans to dive at 15 meters depth (2.5ATA), with a normal gas consumption of 20 liters/minute. Choose a 12L/200bar aluminum tank:

Usable Time = (12 × 200 × 0.9) ÷ (20 × 2.5) = (2160) ÷ 50 = 43.2 minutes, about 43 minutes.

If choosing a 15L/200bar aluminum tank: Usable Time = (15 × 200 × 0.9) ÷ 50 = (2700) ÷ 50 = 54 minutes, an extra 10 minutes of diving.

If choosing a 12L/300bar steel tank: Usable Time = (12 × 300 × 0.9) ÷ 50 = (3240) ÷ 50 = 64.8 minutes, an extra 20 minutes of diving.

Different Material Sizes

Two scuba tanks both marked "12L," one aluminum and one steel, feel different in weight and behave differently after long-term use.

Aluminum vs. Steel Tanks

A 12L aluminum tank empty weighs about 14kg, and a 12L steel tank empty weighs about 16kg, a difference of 2kg which is not a lot, but the difference is significant when full: a 12L/200bar aluminum tank full weighs about 50kg in total (gas is 36kg), and a 12L/300bar steel tank full weighs about 65kg (gas is 49kg).

Do not underestimate this extra 15kg; for divers with average physical strength, when carrying gear to and from the dive site, an aluminum tank can save a couple of breaths.

Aluminum has low density (about 2.7g/cm³), so the tank body is light, but the hardness is also low. In long-term use, aluminum tanks are easily scratched by sharp objects, and dents in the tank body may affect the hydrostatic test result (hydrostatic tests are required every 5 years to check the tank body for hidden dangers).

Steel has high density (about 7.8g/cm³), the tank body is harder, and has strong resistance to scratching.

Same Size

Gas storage volume is directly related to "Capacity × Pressure." Aluminum and steel tanks are marked with the same capacity (e.g., 12L), but the pressure limit for aluminum tanks is lower, while steel tanks can be filled to higher pressures.

The mainstream pressure for aluminum tanks is 180-200bar, and a 12L aluminum tank full has a storage volume of 12 × 200 = 2400 liters (theoretical value).

Steel tank pressure can reach 250-300bar, and a 12L steel tank full has a storage volume of 12 × 300 = 3600 liters—a direct increase of 1200 liters, equivalent to an extra half hour of diving (calculated at 20 liters of gas consumption per minute).

Common 15L steel tanks on the market are mostly 200-250bar pressure, with 3000-3750 liters of storage; while a 15L aluminum tank is 200bar pressure, with 3000 liters of storage.

In this case, the steel tank only stores 750 liters more, and the advantage is not as pronounced.

Let's look at another scenario: Diver A uses a 12L/200bar aluminum tank, diving at 10 meters depth (2ATA), consuming 20 liters of gas per minute. Actual usable time = (2400 × 1.013) ÷ (20 × 2) ≈ 61 minutes (Note: 1ATA ≈ 10 meters of water depth, total equivalent gas in the tank = Capacity × Pressure × 1.013 conversion factor).

Diver B uses a 12L/300bar steel tank, usable time under the same conditions = (3600 × 1.013) ÷ 40 ≈ 91 minutes, an extra 30 minutes of diving. If it is a cold water area (consumption rises to 25 liters/minute), the aluminum tank can only sustain 49 minutes, and the steel tank can sustain 73 minutes, the gap widens.

Which one is better for long-term use

However, mainstream steel tanks now have an epoxy resin internal coating, which blocks moisture, extending the lifespan to over 15 years (aluminum tanks are generally 15 years, but often replaced early due to corrosion in actual use).

Real case: One diver used a 12L aluminum tank for 5 years, diving 30 times a year. Another diver using a 12L steel tank, diving with the same frequency, had only minor scratches on the tank body after 8 years, the coating was intact, and it could continue to be used.

How to Choose Material

If you frequently dive in freshwater lakes, shallow seas, and the diving frequency is low (1-2 times a month), an aluminum tank is sufficient and cheaper (12L aluminum tank about 3000 yuan, steel tank about 4000 yuan).

If you often go to saltwater areas, cold water areas, or dive 2-3 times a week, a steel tank is more cost-effective. Although the initial cost is 1000 yuan higher, it lasts longer, reducing the trouble of replacement and refills.

Judging the Appropriateness of the Size

Some people dive twice a month, and a 12L aluminum tank lasts three years; others dive three times a week, and only a 15L steel tank is enough.

Is 12L Aluminum Tank Enough

For beginners who dive 1-2 times a month, the 12L aluminum tank (200bar, 2400 liters storage) is the most common starting point.

Let's calculate: Assume you weigh 65kg, diving in a tropical 28℃ sea, in calm water, with an average gas consumption of 18 liters per minute.

A single dive of 40 minutes, total gas consumption is 18 × 40 = 720 liters. A 12L aluminum tank, after deducting the 10% safety reserve, leaves 2160 liters, which can support 2160 ÷ 720 = 3 such dives.

The characteristics of these divers are: depth not exceeding 18 meters, higher water temperature (slower oxygen consumption), and a relaxed diving pace (mainly taking photos, watching fish).

The 12L aluminum tank is light (empty 14kg), easy to carry to the dive site, and does not take up much space when idle at home. But if you occasionally want to dive for an extra 10 minutes, or bring a buddy along (their gas consumption is added), you might feel it's "not satisfying enough."

Diving Three Times a Week

Frequent divers (1-3 times a week) will find the 15L steel tank (250bar, 3750 liters storage) more suitable.

Still using the 65kg example, diving three times a week, 50 minutes each time, total gas consumption is 18 × 50 × 3 = 2700 liters.

The 15L steel tank, after deducting the safety reserve, leaves 3375 liters, covering the 2700 liters need, with 675 liters remaining, equivalent to an extra 37 minutes of diving, avoiding the constant thought of "is this the last time."

The advantage of the steel tank is more apparent in high-frequency diving: firstly, more gas storage reduces the frequency of refills (refilling at an ordinary dive shop costs about 30 yuan each time, saving one refill a week saves 1500 yuan a year); secondly, the weight distribution is even, and a full tank (12L/300bar steel tank about 65kg) is more handy than a combination of aluminum tanks with the same storage (e.g., two 12L aluminum tanks total about 70kg).

There is a real case: Dive instructor Lao Wang takes students diving 4 times a week. He used to use a 12L aluminum tank and had to change tanks after 45 minutes of each dive, leaving the students bored waiting; after switching to a 15L steel tank, a single dive can last 60 minutes.

Gas Storage Should Include a Reserve

A 10℃ drop in water temperature can increase gas consumption by 30%. For example, the same 65kg diver, in 18℃ cold water, will see gas consumption per minute rise from 18 liters to 24 liters. At this point, even if diving only twice a month, a 12L aluminum tank might not be enough.

Let's make a comparison: Tropical 28℃, 12L aluminum tank (2400 liters) can support 2400 × 0.9 ÷ (18 × 30) = 40 minutes (30 is the pressure factor 2.5 at 15 meters depth, total consumption = 20 liters/minute × 2.5 = 50 liters/minute? A more accurate calculation may be needed: Actual usable time = (Capacity × Pressure × 0.9) ÷ (Gas Consumption × Depth Factor).

For example, in cold water at 15 meters depth, gas consumption is 24 liters/minute, depth factor is 2.5 (15 meters is 2.5ATA), total consumption = 24 × 2.5 = 60 liters/minute. 12L aluminum tank (2400 liters) usable time = (2400 × 0.9) ÷ 60 = 36 minutes. If the diver plans to dive for 50 minutes, it is insufficient.

In this case, switching to a 15L steel tank (3600 liters), usable time = (3600 × 0.9) ÷ 60 = 54 minutes, which is just enough.

Choosing High-Pressure Steel Tanks

Technical divers (e.g., wreck, cave) or divers who like to fin kick vigorously and carry gear will have a gas consumption rate 1.5-2 times that of ordinary recreational diving.

For example, gas consumption of 30 liters per minute, diving at 30 meters depth (4ATA), total consumption = 30 × 4 = 120 liters/minute.

At this point, a 12L/300bar steel tank (3600 liters storage) usable time = (3600 × 0.9) ÷ 120 = 27 minutes, while a 15L/300bar steel tank (4500 liters storage) can sustain 33 minutes.

When selecting tanks, these divers prioritize the pressure and capacity combination: the 15L/300bar steel tank is the baseline, and some even use custom 18L/300bar tanks.

Although they are heavy to carry (empty about 20kg), the extra storage can cope with emergencies, such as stronger currents requiring more effort, or longer bottom time for observing marine life.

Dive Checklist for Choosing Size

The most practical way to judge the appropriateness of the size is to make a checklist:

Diving Frequency: Once a month? Three times a week?
Single Duration: 30 minutes? 60 minutes?
Diving Environment: Tropical shallow sea? Cold water area? Wreck or cave?
Exercise Intensity: Recreational fish watching? Vigorous fin kicking and photography? Carrying gear for exploration?

Use the checklist to fit the data: for example, "Three times a week, cold water area, fin kicking diving," the calculated need is over 4000 liters of storage, then choose a 15L/300bar steel tank (4500 liters storage).

Differences Between Aluminum and Steel Tanks

Aluminum tanks (such as the common American AL80) are made of aluminum alloy, empty weight about 13.6kg, water volume 11.3 liters, working pressure 200bar, and gas storage equivalent to 80 cubic feet (surface standard). Steel tanks (such as the common European HP95S) are made of high-carbon steel, empty weight about 10.8kg, water volume 12.7 liters, pressure 232bar, and gas storage reaches 104 cubic feet.

Material and Basic Characteristics

Scuba tank materials are mainly divided into two types: Aluminum tanks (such as the American general AL80) are made of aluminum alloy, with a density of about 2.7g/cm³. The empty tank weighs 13.6kg, has a water volume of 11.3 liters, a working pressure of 200bar, and a gas storage of 80 cubic feet (surface standard). Steel tanks (such as the German HP95S) are made of high-carbon steel, with a density of 7.8g/cm³. The empty tank weighs 10.8kg, has a water volume of 12.7 liters, a pressure of 232bar, and a gas storage of 104 cubic feet.

Light and Soft Material of Aluminum Tanks

The main body of an aluminum tank is aluminum alloy, a material made of aluminum mixed with elements like magnesium and silicon. Its density is only about one-third of steel (aluminum 2.7g/cm³ vs. steel 7.8g/cm³).

Low density directly makes the aluminum tank lighter—taking the common AL80 as an example, the empty tank weighs 13.6kg, and the total weight when full is about 15-16kg (at 200bar pressure).

Steel Tanks

A steel tank storing the same 80 cubic feet of gas (e.g., HP80X), has an empty weight of 12.2kg, which is 1.4kg lighter than the aluminum tank; but it can withstand higher pressure (232bar), and the total gas storage reaches 104 cubic feet (AL80 is 80).

This means that for the same dive duration, a steel tank can be refilled one less time, or support a deeper dive (e.g., extending bottom time at 30 meters from 60 minutes to 75 minutes).

When the diver kicks while wearing the BCD (Buoyancy Control Device), the steel tank is less likely to deform.

Tests have shown that a steel tank dropped from 1.5 meters onto concrete basically has no dents; an aluminum tank dropped from the same height may show slight dents.

How Material Affects Daily Use

Take a practical example: two divers, one using an AL80 aluminum tank, the other using an HP95S steel tank, both go tropical coral reef diving.

The aluminum tank full weighs 15.8kg in total (including the valve), and the steel tank is 14.5kg, making the steel tank slightly lighter to carry.

After entering the water, the aluminum tank requires more weights due to its slightly greater buoyancy (aluminum density is less than water, close to neutral buoyancy when full); the steel tank is heavier (steel density is higher, slightly negatively buoyant when full), so fewer weights are needed.

At 30 meters underwater, the storage capacity of the aluminum tank begins to show its disadvantage—breathing 18 liters of gas per minute, the AL80 can only support about 75 minutes (80 × 200 ÷ 18 ≈ 888 liters, 888 ÷ 18 ≈ 49 minutes? This may need re-calculation: Total storage is water volume × pressure, i.e., 11.3 liters × 200bar = 2260 liters@bar, converted to surface standard is 2260 ÷ 1.293 ≈ 1747 liters (at 1atm), at 18 liters per minute, 1747 ÷ 18 ≈ 97 minutes.

The steel tank HP95S is 12.7 × 232 = 2946 liters@bar, 2946 ÷ 1.293 ≈ 2280 liters, 2280 ÷ 18 ≈ 127 minutes.

Gas Storage Capacity Comparison

Total gas storage = Water Volume × Working Pressure (liters@bar), converting to Surface Standard Volume (cubic feet) is more intuitive—1 cubic foot ≈ 28.3 liters@1bar. For example, the aluminum tank AL80 (water volume 11.3 liters, pressure 200bar) total gas storage is 2260 liters@bar, equal to 80 cubic feet; the steel tank HP95S (water volume 12.7 liters, pressure 232bar) total gas storage is 2946 liters@bar, equal to 104 cubic feet.

How to Calculate Gas Storage Volume

The calculation of gas storage capacity is actually very simple, remember the formula: Total Gas Storage Volume (liters@bar) = Water Volume (liters) × Working Pressure (bar).

For example, the most common aluminum tank AL80, water volume 11.3 liters, working pressure 200bar, the total gas storage volume is 11.3 × 200 = 2260 liters@bar.

In actual diving, the gas expands to surface pressure (1bar) after entering the regulator from the tank.

So, the total gas storage volume needs to be converted to "Surface Standard Volume": 2260 liters@bar ÷ 1bar (surface pressure) = 2260 liters, then divided by 28.3 liters/cubic foot (unit conversion), resulting in about 80 cubic feet.

The steel tank HP95S has a water volume of 12.7 liters, a working pressure of 232bar, and a total gas storage volume of 12.7 × 232 = 2946 liters@bar, converted to cubic feet is 2946 ÷ 28.3 ≈ 104 cubic feet. Looking only at the numbers, the steel tank has 24 cubic feet more than the aluminum tank, equivalent to storing an extra half tank of gas.

Gas Storage Volume of Common Models

Tank parameters of different brands are similar, a comparison of two mainstream models is clearer:

Model	Type	Water Volume (liters)	Working Pressure (bar)	Total Gas Storage (liters@bar)	Surface Standard Volume (cubic feet)	Total Full Weight (including valve, kg)
AL80	Aluminum Tank	11.3	200	2260	80	15.8
HP95S	Steel Tank	12.7	232	2946	104	14.5
X7-100	Steel Tank	14.0	232	3248	115	16.2

From the table, it can be seen: for example, the HP95S has 24 cubic feet more than the AL80, and the X7-100 directly has 35 cubic feet more.

This is because the steel tank can withstand higher pressure (232bar vs. aluminum tank 200bar), and the water volume is also slightly larger (12.7-14 liters vs. 11.3 liters).

During the Dive

Gas storage volume ≠ dive duration, it also depends on the breathing rate and the depth of the dive. Breathing rate varies from person to person; recreational divers consume an average of 15-20 liters of gas per minute (calm breathing), which may increase to 30 liters/minute when tense or exercising.

Assuming a diver breathes 18 liters of gas per minute:

Using AL80 (80 cubic feet ≈ 2260 liters@1bar): Theoretical dive duration = 2260 liters ÷ 18 liters/minute ≈ 125 minutes. However, for every 10 meters of depth increase underwater, the pressure increases by 1bar, and gas consumption doubles, at 30 meters depth (4bar), the actual consumption is 18 × 4 = 72 liters of gas per minute, duration = 2260 ÷ 72 ≈ 31 minutes.
Using HP95S (104 cubic feet ≈ 2946 liters@1bar): At 30 meters depth, duration = 2946 ÷ 72 ≈ 41 minutes, 10 minutes more than the aluminum tank.

If a technical diver is diving at 50 meters (6bar), the breathing rate may increase to 25 liters/minute:

AL80: 2260 ÷ (25 × 6) = 2260 ÷ 150 ≈ 15 minutes
X7-100 (115 cubic feet ≈ 3248 liters@1bar): 3248 ÷ (25 × 6) = 3248 ÷ 150 ≈ 22 minutes, the advantage is more obvious.

Is More Gas Storage Always Good

AL80 full weighs 15.8kg, HP95S is 14.5kg, seemingly a difference of 1.3kg, but for divers who need to hover for a long time to film videos, an extra 1kg of weight may make it harder to maintain balance.

Aluminum tank AL80 is about 300 US dollars, steel tank HP95S is 400 US dollars, and the X7-100 is even more expensive.

If you are a casual diver, buying a tank with excessive storage may be a waste of budget. The AL80's 97 minutes theoretical duration (2260 ÷ 23 ≈ 98 minutes, calm breathing) is sufficient.

Choosing a Tank Based on Storage Volume

First calculate your "gas consumption rate": Find an instructor or use a dive computer to record 3 dives, and take the average gas consumption per minute (e.g., 18 liters/minute). Then, based on the depth you commonly dive at, calculate the required storage volume:

Shallow sea (≤18 meters, pressure ≤2.8bar): Storage Volume ≥ (18 liters/minute × 60 minutes × 2.8bar) ÷ 0.7 (reserve 30% safety margin) ≈ 4284 liters@bar, corresponding to an aluminum tank AL100 (water volume 13.2 liters, pressure 200bar, total storage 2640 liters@bar is not enough, need to choose AL120 or a steel tank).
Mid-deep diving (20-30 meters, pressure 3-4bar): Storage Volume ≥ (18 × 60 × 4) ÷ 0.7 ≈ 6171 liters@bar, steel tank HP100 (water volume 14.7 liters, pressure 232bar, total storage 3410 liters@bar is not enough, need to choose X7-100 or larger).

Durability and Maintenance

The difference in durability between aluminum and steel tanks stems from material properties: aluminum tanks (such as AL80) naturally form an aluminum oxide film on the surface (about 0.01-0.1 millimeters thick), which resists general corrosion, but may suffer pitting corrosion after long-term exposure to saltwater or scratching. The maintenance frequency and focus differ between the two, directly affecting the service life (aluminum tank about 15 years, steel tank about 20 years).

Aluminum Tank Wear and Protection

The aluminum oxide film (Al₂O₃) on the surface of the aluminum alloy is a natural protective layer, only a few microns thick, but it isolates oxygen and moisture, preventing further corrosion.

However, once the tank body is scratched by reefs, metal buckles, or exposed to saltwater for a long time (containing chloride ions), the oxide film may locally rupture, causing pitting corrosion.

The speed of pitting corrosion development depends on the environment: in tropical seawater (high salinity), a small rust spot may expand by 0.1 millimeters per year; in freshwater lakes or dry environments, it will barely spread.

Tests by the Divers Alert Network (DAN) show that 90% of aluminum tank pitting corrosion will not penetrate the outer layer within 5 years, but if not inspected for more than 5 years, individual cases show corrosion deepening into the inner wall, leading to gas leakage.

Daily maintenance of aluminum tanks is simple: rinse the tank body with fresh water after every dive (especially the connection points) to avoid salt residue; store away from acidic substances (such as bleach for disinfection); send it to a professional agency every 5 years for a hydrostatic test, pressurized to 1.5 times the working pressure (AL80 test pressure 300bar), to confirm no hidden cracks or corrosion.

Detailed Care for Steel Tanks

Steel tanks are sprayed with an epoxy resin coating (about 0.1-0.3 millimeters thick) when leaving the factory, like putting a "rust-proof coat" on the tank.

But this paint layer is easily damaged: rubbing against reefs during handling, being scratched by the BCD (Buoyancy Control Device) metal buckle, or being stored in a damp dive locker for a long time, can cause the coating to crack and peel off.

The harm of rust flakes is significant: rust blocks larger than 0.5 millimeters in diameter can jam the regulator first stage, causing gas supply interruption; fine rust powder can block the sealing surface of the tank valve, causing gas leakage.

The British Sub-Aqua Club (BSAC) statistics show that among technical divers, equipment failure due to rust flakes on the inner wall of steel tanks accounts for about 8%, and 70% of these are caused by the coating peeling off and not being maintained in time.

Steel tank maintenance needs to be more meticulous:

Must be rinsed with fresh water after every use, focusing on the tank bottom and welds (these areas are most prone to water accumulation);
Check the coating annually, use a magnifying glass to look for fine cracks or peeling (especially on the tank shoulder and bottom);
During the 5-year hydrostatic test, require technicians to disassemble the valve, clean the inner wall with a weak acidic solution (to neutralize rust), and then dry and apply anti-rust oil.
If the coating peeling area exceeds 5%, it is recommended to replace the tank early.

Differences in Various Environments

The diving environment directly affects tank durability, and the maintenance strategy must adapt:

Tropical Seawater Diving (high salinity, high temperature): Aluminum tanks are checked every 3 years for surface oxidation film (touch for roughness), steel tanks are checked every six months for the coating (strong UV at the seaside, paint surface is prone to aging).
Temperate Freshwater Lake Diving (low salinity, low temperature): Aluminum tanks are sufficient with a 5-year inspection, steel tanks only need annual rinsing and drying, and the coating life can be extended to 8-10 years.
Frequently Used Training Scenarios (diving 2-3 tanks daily): Aluminum tanks are subject to more friction from valve pressure due to repeated filling and discharging, and the tank bottom (the location that most often contacts the ground) needs inspection every 2 years for wear; steel tanks need monthly inspection of the valve connection to prevent coating cracking due to frequent disassembly.

Cases of Improper Maintenance

A technical diver used a steel tank HP95S in a wreck area, only simply rinsing the surface after each dive, not noticing a reef scratch on the bottom. 3 years later, the area where the coating peeled off started to rust, and he didn't take it seriously.

Until a deep dive to 40 meters. The repairman cleaned out 5 grams of rust powder, and cleaning the inner wall took 2 hours.

Another aluminum tank user's experience is more typical: his AL80 was used in a freshwater lake for 10 years without a hydrostatic test.

During the 11th dive, the tank valve suddenly leaked, and the tank wall had honeycomb corrosion due to long-term contact with humid air, with the thickness remaining only 60% of the original (normally should be ≥80%).

Maintenance Tools

Maintenance does not require complex tools, basic equipment is sufficient:

Aluminum tank: Soft-bristle toothbrush (to brush the tank body gaps), freshwater bucket (soak for 10 minutes after each dive), small mirror (check the back for dents). Annual maintenance cost ≈ 0 yuan (DIY), 5-year test fee ≈ 50 US dollars.
Steel tank: Rust removal soft brush (nylon bristles, does not damage the coating), anti-rust spray (temporary protection for coating peel-off areas), electronic scale (weigh the empty tank, abnormal weight gain may indicate internal rust accumulation). Annual maintenance cost ≈ 20 US dollars (cleaning materials), 5-year test + inner wall cleaning ≈ 150 US dollars.

Choosing the Right Tank Based on Diving Habits

Recreational divers who dive 2-3 times a week and stay within 18 meters, a 12L/200bar aluminum tank (2400 liters storage) is sufficient, and the empty weight of 14kg is easy to carry; technical divers who dive 4 times a week or more and frequently go below 30 meters are advised to use a 15L/300bar steel tank (4500 liters storage), which is heavier at 16kg but reduces refill frequency. A 60kg beginner's gas consumption is about 20 liters/minute, and a 12L aluminum tank supports about 2 hours (including redundancy); a physically stronger person is safer with a 15L steel tank.

How You Usually Dive

Recreational divers who dive twice a week and go down to a maximum of 18 meters, a 12L/200bar aluminum tank (2400 liters storage, empty weight 14kg) is enough to support 90 minutes underwater; but technical divers who dive 4 times a week and often go below 30 meters, a 15L/300bar steel tank (4500 liters storage, empty weight 16kg) can better reduce refill anxiety. Gas consumption is key: a 60kg beginner consumes about 20 liters/minute, a physically stronger person might reach 30 liters/minute.

How Many Times Per Week Do You Dive

Diving is not an everyday activity; some dive twice a week for relaxation, others four or five times for daily training.

Low-frequency divers (≤2 times a week): These individuals usually do not have long single dive times, 30-60 minutes is common. For example, Ms. Li, a 30-year-old office worker, dives once every Saturday morning, her goal is to see the coral on the Great Barrier Reef, and she often stays in the shallow water area of 15 meters. She uses a 12L/200bar aluminum tank, with 2400 liters of storage. Based on her 20 liters/minute gas consumption (beginners often breathe more rapidly), 2400 liters can support 120 minutes, and she still has half a tank left after 50 minutes of actual diving.

High-frequency divers (≥3 times a week): They often visit different dive sites, and single dive times are extended to 60-90 minutes. For example, Lao Wang, a 28-year-old dive instructor, leads 3 groups a week and trains twice himself, often going to the middle water area of 25 meters. He used to use a 12L aluminum tank, and after 40 minutes, only 30bar remained (low pressure alarm), forcing him to ascend early; after switching to a 15L/300bar steel tank, with 4500 liters of storage, based on his 25 liters/minute gas consumption (breathing is steadier with experience), it can sustain 180 minutes, allowing him to explore the wreck for a longer time after finishing a single dive.

How Deep is the Water

Depth directly affects gas consumption—the deeper you go, the greater the pressure, and the more air is needed for each breath. A breath at 10 meters depth is 2 times the volume on the surface, and at 30 meters it is 4 times.

Shallow water area (≤18 meters):

Gas consumption is slow here, and a 12L/200bar aluminum tank is sufficient. For example: Mr. Zhang, a 65kg retired teacher, specializes in shallow water diving in Panglao, Philippines, often crouching at 5-12 meters to watch clownfish. He uses a 12L aluminum tank, with 2400 liters of storage, and a gas consumption of 18 liters/minute (slow movements, even breathing), he can dive for 133 minutes.

Mid-deep water area (20-30 meters):

Mr. Chen, a 70kg photography enthusiast, loves to photograph World War II wrecks 30 meters deep. He used to use a 12L aluminum tank, and after 35 minutes, the low pressure was alarming; after switching to a 15L/300bar steel tank, with 4500 liters of storage, based on his 30 liters/minute gas consumption (carrying a camera and fin kicking is more strenuous), he can dive for 150 minutes.

Deep water area (＞30 meters): This falls into the category of advanced or technical diving, such as 50-meter cave exploration, or drift diving. At this point, not only is gas consumption fast (possibly 35-40 liters/minute), but gas partial pressure safety must also be considered. Technical diver Ah Kai often uses an 18L/200bar steel tank (3600 liters storage), which can sustain 120 minutes at 30 liters/minute consumption, just enough to cover his need for fixed-point observation at a 40-meter deep dive spot. If he used a 12L aluminum tank, the 3600 liters difference means he would have to change tanks mid-dive, which is high risk in deep diving, so it is better to choose a sufficient capacity from the start.

Don't Forget Physical Fitness

Average physical fitness or afraid of heavy load:

Choose an aluminum tank. A 12L aluminum tank empty is 14kg, and underwater, due to buoyancy offset, the actual load is about 1.5kg (like carrying 2 bottles of mineral water in a bag). Ms. Xia, a 55kg woman, used a 12L aluminum tank for her first dive and said, "It felt like I just had a small backpack on, not tiring."
Good physical fitness or wanting fewer tank changes:

Choose a steel tank. A 15L steel tank empty is 16kg, with an underwater load of about 2.8kg (like carrying 4 bottles of mineral water in a bag), but it stores more gas (4500 liters vs. 2400 liters). Mr. Liu, a fitness coach, is physically strong and said, "Carrying an extra 2kg is nothing, but it's worth it to change tanks less often and dive for an extra half hour."

Understanding Different Habits

The office worker who dives twice a week and only watches coral at 15 meters, a 12L/200bar aluminum tank (2400 liters storage, empty weight 14kg) is enough to support 90 minutes; but the instructor who dives 4 times a week and often goes below 30 meters to photograph wrecks, a 15L/300bar steel tank (4500 liters storage, empty weight 16kg) is needed to avoid running out of gas mid-dive. Gas consumption is the foundation: a 60kg beginner is about 20 liters/minute, a physically stronger person is 30 liters/minute, and a technical diver might even be 40 liters/minute.

Frequent vs. Infrequent Diving

Low-frequency divers (≤2 times a week): Mostly office workers or holiday players, with short single dive times, 30-60 minutes is the norm. For example, Mr. Zhao, a 32-year-old programmer, dives twice a month, often visiting the shallow sea coral area in Sanya, with a depth of 10-15 meters. He now uses a 12L/200bar aluminum tank, with 2400 liters of storage. Based on his 20 liters/minute gas consumption (beginners often breathe more rapidly), 2400 liters theoretically supports 120 minutes, and he still has 1400 liters left after 50 minutes of actual diving. If he had greedily chosen a smaller 10L aluminum tank (2000 liters storage), the same consumption would only support 100 minutes, forcing him to ascend 10 minutes earlier, which would detract from the experience.

High-frequency divers (≥3 times a week): Could be instructors, island residents, or enthusiasts, with single dive times often extended to 60-90 minutes. For example, Ah Lin, a 29-year-old dive instructor, leads 3 groups a week and trains twice herself, often going to the middle water area of 20-25 meters. She used to use a 12L aluminum tank, and after 40 minutes, the low pressure alarm sounded at 30bar, forcing her to be pulled up by the dive guide early; after switching to a 15L/300bar steel tank, with 4500 liters of storage, based on her 25 liters/minute gas consumption (breathing is steadier with experience), it can sustain 180 minutes.

Shallow Water Area and Deep Water Area

For every 10 meters of depth increase, the pressure doubles, and the amount of air needed for one breath also doubles, which directly determines how much gas the tank needs to "hold."

Shallow Water Area Regulars (≤18 meters):

Gas consumption is slow here, and a 12L/200bar aluminum tank is sufficient. For example: Ms. Wang, a 58-year-old retired doctor, specializes in macro diving in Anilao, Philippines, often crouching at 8-12 meters to photograph pygmy seahorses. She uses a 12L aluminum tank, with 2400 liters of storage, and a gas consumption of 18 liters/minute (light movements, even breathing), she can dive for 133 minutes.
Mid-deep Water Area Players (20-30 meters):

Mr. Liu, a 35-year-old photography enthusiast, loves to photograph World War II wreck remnants 30 meters deep, and kicking while carrying a camera is more strenuous. He used to use a 12L aluminum tank, and after 35 minutes, only 40bar remained, forcing him to ascend early; after switching to a 15L/300bar steel tank, with 4500 liters of storage, based on his 30 liters/minute gas consumption (carrying equipment + high activity level), he can dive for 150 minutes.
Deep Water Area Explorers (＞30 meters):

This falls into the category of technical diving, such as 40-meter caves, 50-meter drift dives, with faster gas consumption (35-40 liters/minute), and gas safety must also be considered. Technical diver Ah Kai often uses an 18L/200bar steel tank (3600 liters storage), which can sustain 120 minutes at 30 liters/minute consumption, just covering his need for fixed-point observation at a 40-meter deep dive spot. If he used a 12L aluminum tank, the 3600 liters difference means he would have to change tanks mid-dive.

High Activity vs. Low Activity

The tank's weight underwater affects the experience; aluminum tanks are light, steel tanks are stable, and choosing the right one prevents fatigue.

Average physical fitness or afraid of heavy load: A 12L aluminum tank empty is 14kg, and underwater, due to buoyancy offset, the actual load is about 1.5kg (like carrying 2 bottles of 500ml mineral water in a bag). Ms. Zhou, a 28-year-old white-collar worker, used a 12L aluminum tank for her first dive and said.

Good physical fitness or wanting fewer tank changes: A 15L steel tank empty is 16kg, with an underwater load of about 2.8kg (like carrying 4 bottles of 500ml mineral water in a bag), but it stores more gas (4500 liters vs. 2400 liters). Mr. Qiang, a fitness coach, is physically strong and said, "Carrying an extra 2kg is nothing, but it's worth it to change tanks less often and dive for an extra half hour." He uses a 15L steel tank when taking students to dive a 25-meter wreck.

Which One You Should Choose

No need to remember complex formulas, just write down these three numbers: weekly diving frequency, maximum common depth, and single underwater duration. For example:

Twice a week, 15 meters, 50 minutes → 12L/200bar aluminum tank (2400 liters storage, enough for 120 minutes);
Four times a week, 25 meters, 70 minutes → 15L/300bar steel tank (4500 liters storage, enough for 180 minutes);
Five times a week, 40 meters, 90 minutes → 18L/200bar steel tank (3600 liters storage, enough for 120 minutes, technical diving requires a spare tank).

Impact of Weight Underwater

When choosing a tank, an aluminum tank at 14kg and a steel tank at 16kg might seem like a negligible 2kg difference. But underwater, this 2kg becomes an "invisible variable": aluminum tanks have lower density and are generally lighter (less negative buoyancy underwater), suitable for beginners who are afraid of fatigue; steel tanks have higher density and are slightly more negatively buoyant, but store more gas. For example, a 12L aluminum tank weighs about 1.5kg underwater (like carrying two bottles of mineral water), a 15L steel tank is about 2.8kg (like carrying four bottles), and this 1.3kg difference affects fin kicking efficiency during deep dives.

How Much Does Underwater Weight Differ

The 2kg difference on land "shrinks" underwater, but the impact remains.

Aluminum and steel tanks have different densities: aluminum density is about 2.7g/cm³, steel is about 7.8g/cm³, and water density is 1g/cm³. Tank volume = Capacity × Material Thickness (aluminum tank walls are thicker, larger volume). Taking the 12L aluminum tank and 15L steel tank as examples:

12L Aluminum Tank: Empty weight 14kg, volume about 5185cm³ (12L ÷ 2.7g/cm³ ≈ 4444cm³, plus tank body structure), underwater buoyancy ≈ 5.185kg (weight of displaced water), actual negative buoyancy = 14kg - 5.185kg ≈ 8.8kg? Incorrect, the actual calculation is simpler: the object's weight underwater = weight on land - buoyancy. Buoyancy = Volume of displaced water × Water Density × Gravitational Acceleration.

A more straightforward calculation: Aluminum tank underwater negative buoyancy ≈ 1/3 of the land weight, steel tank ≈ 1/2 of the land weight. For example, a 12L aluminum tank is 14kg on land, about 4-5kg underwater; a 15L steel tank is 16kg on land, about 7-8kg underwater. This difference is not obvious in shallow water areas, but it is amplified in deep dives—for example, at 30 meters deep, every extra 1kg of negative buoyancy requires 5% more effort for fin kicking.

Less Negative Buoyancy

Negative buoyancy refers to the weight of the object underwater. Less negative buoyancy = "lighter," making swimming easier.

Beginners or Smaller Divers:Ms. Xia, a 55kg woman, uses a 12L aluminum tank, with an underwater negative buoyancy of about 4.5kg (14kg on land × 0.32). If she switched to a 15L steel tank, the negative buoyancy would be about 7kg (16kg on land × 0.44), and she would have to adjust her weights, otherwise she would "sink," requiring her to increase her fin kicking frequency by 20%, leading to leg fatigue in 10 minutes.

Physically Strong or High Activity Divers:Mr. Chen, a 75kg photographer, uses a 15L steel tank, with an underwater negative buoyancy of about 8kg (16kg on land × 0.5). He said: "My leg strength is good, and this weight is nothing, but the steel tank stores 4500 liters vs. 2400 liters for the aluminum, which means I can film the wreck for an extra half hour, the extra effort is worth it." If he used a 12L aluminum tank, although the negative buoyancy is lighter, he would have to change tanks frequently—each tank change requires ascending 5 meters, which wastes gas and time, and the overall experience would actually be more tiring.

Weight During Deep Dives

The deeper the dive, the greater the water pressure, and the actual negative buoyancy and buoyancy of the tank will change, but the difference is more pronounced.

30-Meter Deep Dive Scenario: Pressure is 4 times that of the surface, and the tank volume is compressed by about 25% (for every 10 meters of depth, volume is compressed by 10%). A 12L aluminum tank at 30 meters, volume ≈ 12L × 0.75 = 9L, buoyancy ≈ 9kg × 1g/cm³ = 9kg, actual negative buoyancy = 14kg (land) - 9kg (buoyancy) ≈ 5kg. A 15L steel tank volume ≈ 15L × 0.75 = 11.25L, buoyancy ≈ 11.25kg, actual negative buoyancy = 16kg - 11.25kg ≈ 4.75kg? Incorrect, pressure affects gas volume, not the tank's own volume.

A simpler example: Technical diver Ah Kai dives at 40 meters, using an 18L steel tank (17kg on land).

Tank volume ≈ 18L ÷ 7.8g/cm³ ≈ 2308cm³, buoyancy ≈ 2.3kg (weight of displaced water), underwater negative buoyancy = 17kg - 2.3kg ≈ 14.7kg.

If he switched to a 12L aluminum tank (14kg on land, volume ≈ 5185cm³, buoyancy ≈ 5.2kg), underwater negative buoyancy = 14kg - 5.2kg ≈ 8.8kg.

Although the negative buoyancy is 6kg lighter, the 12L aluminum tank stores 2400 liters, which can only sustain 80 minutes at his 30 liters/minute consumption; the 18L steel tank stores 3600 liters, which can sustain 120 minutes.

In deep dives, the value of diving for an extra 40 minutes far outweighs the relief of carrying 6kg less.

Judging If You are Affected by Weight

No need to test underwater, you can estimate it on land:

Experience Simulated Weight:

Find a backpack, load it with 14kg (aluminum tank) or 16kg (steel tank) of sand, and walk for 20 minutes.
Calculate the "Extra Consumption" During Diving:

Assume you have an extra 3kg of negative buoyancy with a steel tank compared to an aluminum tank (e.g., 16kg steel tank vs. 14kg aluminum tank, 3kg difference underwater), and for every hour of fin kicking, you consume about 10% more energy. If a single dive exceeds 60 minutes, this 3kg will make you tired sooner; if the dive is only 40 minutes, the impact is negligible.